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[vm] ☂️ @pragma('vm:deeply-immutable') #55120

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dcharkes opened this issue Mar 6, 2024 · 1 comment
Open
3 tasks

[vm] ☂️ @pragma('vm:deeply-immutable') #55120

dcharkes opened this issue Mar 6, 2024 · 1 comment
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area-vm Use area-vm for VM related issues, including code coverage, and the AOT and JIT backends. type-enhancement A request for a change that isn't a bug

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@dcharkes
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dcharkes commented Mar 6, 2024 •
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Filing a tracking issue for expanding the feature-set of @pragma('vm:deeply-immutable').

https://dart-review.googlesource.com/c/sdk/+/354902 Introduces basic functionality.

  • Deeply immutable classes can have fields which are deeply immutable.
  • Deeply immutable classes can extend other deeply immutable classes.
  • Allow type parameter types in fields of deeply immutable classes.

Not covered in this CL, but could be covered:

  • Allow using deeply immutable classes across libraries.
  • Allow mixin in deeply immutable classes. (Requires allowing deeply immutable classes across libraries, mixins can't be final or sealed.)
  • Allow record types in fields of deeply immutable classes.
@dcharkes dcharkes added the area-vm Use area-vm for VM related issues, including code coverage, and the AOT and JIT backends. label Mar 6, 2024
@a-siva a-siva added the type-enhancement A request for a change that isn't a bug label Mar 6, 2024
@dcharkes
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dcharkes commented Mar 7, 2024

Note that the deeply immutable bit is lost in AppJIT snapshots currently:

This doesn't really matter for the use case with native finalizers (#55062 (comment)), because pointers to native memory cannot be part of snapshots.

copybara-service bot pushed a commit that referenced this issue Mar 7, 2024
@dcharkes
[vm] Introduce pragma vm:deeply-immutable
8de00e2 
This CL introduces a way to mark all instances of a class as deeply
immutable.

In order to statically verify that all instances of a deeply immutable
class are immutable, a deeply immutable classes must have the following
properties:

1. All instance fields must
   1. have a deeply immutable type,
   2. be final, and
   3. be non-late.
2. The class must be `final` or `sealed`. This ensures no
   non-deeply-immutable subtypes are added by external code.
3. All subtypes must be deeply immutable. This ensures 1.1 can be
   trusted.
4. The super type must be deeply immutable (except for Object).

Note that instances of some classes in the VM are deeply immutable
while their class cannot be marked immutable.

* SendPort, Capability, RegExp, and StackTrace are not `final` and
  can be implemented by external code.
* UnmodifiableTypedDataViews do not have a public type. (It was
  recently deprecated.)

See runtime/docs/deeply_immutable.md for more details.

Use case:

This enables attaching a `Dart_FinalizableHandle` to a deeply immutable
object and the deeply immutable object with other isolates in the same
isolate group.

(Note that `NativeFinalizer`s live in an isolate, and not an isolate
group. So this should currently _not_ be used with `NativeFinalizer`s.
See #55062 for making a
`NativeFinalizer.shared(` that would live in an isolate group instead
of in an isolate.)

Implementation details:

Before this CL, the `ImmutableBit` in the object header was only ever
set to true for predefined class ids (and for const objects). After
this CL, the bit can also be set to true for non const instances of
user-defined classes. The object allocation and initialization code has
been changed to deal with this new case. The immutability of a class is
saved in the class state bits. On object allocation and initialization
the immutability bit is read from the class for non-predefined class
ids.

TEST=runtime/tests/vm/dart/isolates/fast_object_copy2_test.dart
TEST=runtime/vm/isolate_reload_test.cc
TEST=tests/lib/isolate/deeply_immutable_*

Bug: #55120
Bug: #54885
Change-Id: Ib97fe589cb4f81673cb928c93e3093838d82132d
Cq-Include-Trybots: luci.dart.try:vm-aot-android-release-arm64c-try,vm-aot-android-release-arm_x64-try,vm-aot-linux-debug-x64-try,vm-aot-linux-debug-x64c-try,vm-aot-mac-release-arm64-try,vm-aot-mac-release-x64-try,vm-aot-obfuscate-linux-release-x64-try,vm-aot-optimization-level-linux-release-x64-try,vm-appjit-linux-debug-x64-try,vm-asan-linux-release-x64-try,vm-checked-mac-release-arm64-try,vm-eager-optimization-linux-release-ia32-try,vm-eager-optimization-linux-release-x64-try,vm-ffi-android-debug-arm-try,vm-ffi-android-debug-arm64c-try,vm-ffi-qemu-linux-release-arm-try,vm-ffi-qemu-linux-release-riscv64-try,vm-fuchsia-release-x64-try,vm-kernel-linux-debug-x64-try,vm-kernel-precomp-linux-release-x64-try,vm-linux-debug-ia32-try,vm-linux-debug-x64-try,vm-linux-debug-x64c-try,vm-mac-debug-arm64-try,vm-mac-debug-x64-try,vm-msan-linux-release-x64-try,vm-reload-linux-debug-x64-try,vm-reload-rollback-linux-debug-x64-try,vm-ubsan-linux-release-x64-try
Cq-Include-Trybots: dart-internal/g3.dart-internal.try:g3-cbuild-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/354902
Commit-Queue: Daco Harkes <dacoharkes@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>
copybara-service bot pushed a commit that referenced this issue Mar 11, 2024
@dcharkes
[vm/ffi] Example with deeply-immutable Finalizable and dart_api_dl
8682ca7 
A test exercising isolate group finalizers with `Finalizable` and
`pragma('vm:deeply-immutable')`.

Note that we cannot fully do without C code due to the signature of
`Dart_HandleFinalizer` which also passes a
`void* isolate_callback_data` in addition to the peer.

TEST=tests/ffi/deeply_immutable_c_api_finalizer_test.dart

Bug: #55062
Bug: #55120
Change-Id: Ibaf4899ca678ffb0c5d227ac4f10deb38d49fe6f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/356720
Reviewed-by: Martin Kustermann <kustermann@google.com>
Reviewed-by: Hossein Yousefi <yousefi@google.com>
Commit-Queue: Daco Harkes <dacoharkes@google.com>
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